The Catholic-backed sympto-thermal method of natural family planning has been found by a German study to be as effective in preventing pregnancies as the contraceptive pill, with researchers also surprised to find a low rate of unintended pregnancies among women who had unprotected sex during their fertile period.

The study was published on 21 February in an online report in the European reproductive medicine journal named "Human Reproduction Today" by researchers from the University of Heidelberg, Earthtimes reports.

From 1985 to 2005, the German Natural Family Planning study centre observed 1599 women who used sympto-thermal method (STM). The data collected from 900 of these women, involving 17,638 menstrual cycles formed the basis of their study.

The STM form of family planning involves measuring the temperature of a woman and watching cervical secretions during her fertile phase.

During this period she then abstains from sex or the use of other contraception methods.

Three hundred and twenty two of these 900 women used STM, 509 women practiced STM interspersed with other barriers during fertility phase, and 69 of the women failed to document their sexual behavior.

The women involved in the study sent the researchers charts showing their cycles, records of their temperature, their cervical secretions, the sexual behaviour and what their family planning objectives for the next cycle were, every month.

The study revealed that couples abstaining from sex or using a barrier method during this time had unplanned pregnancies as low as 0.4 per cent - 0.6 per cent every year.

Women having unprotected sex during the fertile phase of thirteen cycles resulted in pregnancy rates of 7.5 per cent.

The low rates of unintended pregnancies (7.5 per cent) in spite of unprotected sex during the fertile phases surprised the researchers and led Prof Frank-Herrmann and team members to believe that the couples were observing "conscious, intelligent risk-taking".

She further remarked that in order for STM to be effective precise rules must be observed. The method requires time be spent in learning it through a book, consulting a qualified teacher or attending a NFP course. It also requires more involvement.

Toni Belfield, of the Family Planning Association (FPA), remarked in this context, "Natural family planning when taught properly and carried out correctly is a highly effective method of family planning.

According to Earthtimes, the divorce rate of couples practising NFP is just 5 per cent.